Implants (implantable medical devices, IMD) such as cardiac pacemakers, defibrillators, and neurological devices like deep brain stimulators for deep brain stimulation, spinal cord stimulators, TENS (transcutaneous electrical nerve stimulators), devices for muscular stimulation therapy, and diagnostic equipment that tests the chemical properties of the blood of the patient, other body parts, or other properties and parameters of the body, frequently use electrode leads that are guided into the patient's body and remain there for at least the treatment or measurement period. Electrode leads are connected to the implant in an electrically conducting manner.
The implants normally include a biocompatible housing having an associated electronic circuit and an energy supply, e.g., a battery. The housing has a socket to which one or a plurality of electrode leads may be connected, for example, by means of a plug. Electrode leads transmit the electrical energy or data from the housing to the part of the body being treated or examined or vice versa.
In the context of the present invention, the term “electrode lead” shall be construed to mean a lead having an electric conductor or a plurality of electric conductors together with the enclosing insulating tube, which electrically insulates the electrical conductors from the outside and one another, and all of the other functional elements that are securely connected to the lead. As a rule, at its distal end, the electrode lead also comprises a so-called electrode tip, by means of which the electrical energy is introduced from the conductor(s) into the tissue to be treated. Frequently, an electrode tip is provided with anchor elements or retaining structures with which the physical position of the transition point for the electrical energy into the tissue to be treated is kept constant. The electrode tip may be embodied as a recording electrode, stimulating electrode, or measuring electrode. In addition, as a rule the electrode lead has, for instance at its proximal end, a plug with which the electrode lead may be connected to an implant, wherein for this the plug is inserted into a corresponding socket in the implant. The plug has one or a plurality of connectors, wherein each connector is connected with precisely one electrical conductor of the electrode lead. Correspondingly, in the socket, one connector of the socket is provided for each connector of the electrode lead.
Frequently, a plurality of electrode leads are connected to modern implants, for instance a multichamber cardiac pacemaker. In this case, efforts are made to configure the electrode leads and their connectors as thin and small as possible. However, this makes it more difficult to provide the plugs and connectors with easily visible markings and to differentiate the electrode leads. Moreover, as the number of electrode leads increases, so does the risk that individual electrode leads will be confused and/or incorrectly attached. It is therefore desirable for an implant to detect which electrode leads are connected so that it may actuate them appropriately. In addition, for operating the implant it is helpful when the electrode leads and/or their properties are identifiable for the implant.
U.S. Publication No. 2004/0073265 describes a device that provides an opportunity to detect incorrectly connected coronary leads and/or incorrect connections to cardiac rhythm management devices. To this end, a voltage introducing device of a pacemaker generates a voltage pulse between an electrode that is connected to a lead of the pacemaker and a head or housing electrode of the pacemaker. The housing electrode transmits a connection signal. The electrode is used to measure a corresponding connection signal using the lead. A measuring module of the device also measures one or a plurality of properties of the corresponding connection signal, such as current strength, voltage, impedance, and/or its time delay (after outputting the voltage pulse). The signal properties may be influenced by one or a plurality of leads and/or by intervening tissue and fluids (for example, a heart, including one or more of its chambers) disposed therebetween. A comparison module of the pacemaker may then establish whether the lead is properly guided to a contact of the pacemaker, wherein one or a plurality of properties of the corresponding connection signal are compared to appropriate preselected ranges of values. For instance, a measured impedance may be compared to an expected impedance range. The device described in the document thus does not selectively identify the lead, but on the contrary tests whether, following excitation of the body by a voltage pulse of a housing electrode for the pacemaker, the corresponding comparison signal received via a lead has properties within a prespecified range. The properties of the corresponding comparison signal are also determined by the excited body tissue between the housing electrode of the pacemaker and the receiving electrode. Only gross deviations, like those that occur due to a non-connected or completely incorrect type of lead, may be traced back to the lead with certainty; smaller deviations may be caused by the body. The aforesaid device therefore cannot provide the reliable and intentional detection of and differentiation between electrode leads having similar properties.
U.S. Publication No. 2006/0212083 also discloses a similar device. In this document, as well, it is stressed that the signal properties are influenced by the leads and/or by the intervening tissue or fluid disposed therebetween.
U.S. Publication No. 2011/0112609 describes a system for spinal cord stimulation having at least one implantable stimulating lead. It comprises, in particular, a medical programming device and an implantable pulse generator that is connected to one or to a plurality of implantable stimulating leads, each of which have a plurality of electrodes. The stimulating lead has one or two lead bodies. The electrodes fit precisely into the epidural space in the spinal column. Since the tissue there is conductive, electrical measurements may be taken between the electrodes. A control circuit of the implantable pulse generator takes such electrical measurements so that the medical programming device can automatically identify the individual lead bodies that are connected to the implantable pulse generator. The electrical measurements of the control circuit for identifying the connected lead bodies are field potentials. The control circuit may also measure the impedance at each electrode in order to determine the coupling efficiency between each electrode and the tissue and to determine the error detection for the connection between the electrode and the analog output circuit for the implantable pulse generator. In the known system, it is a drawback that the identification is not performed using the implantable pulse generator itself, but instead using an additional medical programming device.
U.S. Publication No. 2012/0123496 has to do with connectivity detection and type identification of an implanted lead for an implantable medical device. The device has a processor that can determine the connection and the type of lead. First, a signal measuring module tests the connection of the leads in that it tests values of electrical parameters during a signal between at least two electrodes, especially the impedance. One or more leads may have active electronics integrated therein that include one or more modular circuits integrated therein, depending on whether the lead is unipolar or multipolar. Each of the modular circuits is able to control a plurality of electrodes of the lead and includes a circuit arrangement that is connected electrically to one or a plurality of electrodes of the lead. As such, each of the modular circuits of a lead acts as an interface between the implanted medical device and the electrodes to which the modular circuit is connected. For measuring the impedance, the processor of the device controls the modular circuit such that the latter supplies a voltage pulse between a first and a second electrode. The signal measuring module measures the resulting current and the processor derives the impedance from this. In another step, the processor sends a query signal along a first conductor of the lead in order to obtain a reply about a second lead from the modular circuits. Such a response from each modular circuit supplies the processor information about the modular circuit and the electrodes it controls. In another configuration step, the processor transmits a signal via the first lead. The configuration step includes that the active configuration of the modular circuit is programmed. Refer to U.S. Pat. No. 7,713,194 for lead embodiments and active electronics and the modular circuits used therein. According to this publication, the modular circuit is embodied such that it is controlled via a bus. U.S. Publication No. 2012/0123496 consequently describes that the additional interface electronics of the modular circuits may be detected and thus the electrode lead may be determined. It is a drawback of the known device that complex modular circuits having active electronics for controlling the electrodes must be implemented and programmed. Furthermore, the information relates only to the modular circuits and the electrodes connected thereto, but not the lead as a whole.
U.S. Publication No. 2003/0018369 depicts a method and a device for automatically detecting and configuring implantable medical leads. For this method, a first communication circuit that stores data, such as model number and serial number, technical information, and calibration data, is connected to the lead or integrated therein. It has a receiver and a transmitter for receiving data signals from an external source. Thus, it may be programmed with identification data, calibration data, and other data during production. The first communication circuit is embodied as a passive transponder, and, in addition to the receiver and transmitter, also has an energy coupler for supplying energy and a control circuit that is connected to a non-volatile memory. The control circuit delivers the lead information stored in the memory to the transmitter/receiver of the transponder, which transmits the data via RF or other communication. During implantation of the lead, or thereafter, the information may be transferred to a second communication circuit outside of the lead. The transferred data may be used for identifying the lead, may be recorded in a patient file, and may be transferred to a central memory for use by the health service provider. Using the transponder, the lead may be detected automatically and the data stored in the memory may be transferred directly and forwarded. In addition to a transmitter and receiver, however, the transponder also needs a separate energy supply, a control unit, and a programmable digital memory. Because of this, the overall structure of the lead is relatively complex and expensive.
U.S. Publication No. 2014/0343633 also represents an electrically identifiable electrode lead having an identification module that has at least one filter, a current converter, a communication circuit, a load circuit, and a memory unit, such as an EPROM, for storing an identification code. Before the implant is inserted, each lead is implanted and connected to the implantable pulse generator (or an external pulse generator) that then retrieves self-identifying data from the identification module and can transmit this information to an external device like the medical programmer. The identification module can store up to 32 bytes of data for this. This method is repeated for each lead that is implanted. The identification module uses two available contacts of the lead for connecting to the implantable pulse generator. As in the aforesaid document, a digital memory is also required for this known electrode lead and the structure of the identification module is similarly complex.
Known from U.S. Publication No. 2006/0212096, U.S. Publication No. 2008/0065181, and U.S. Pat. No. 7,983,763 are devices for identifying an implantable medical device and an implantable conductor system in which an RFID tag having an RFID chip is arranged in the insulation surrounding the conductor or in the header block of an implantable device. Furthermore, a read device is provided that can wirelessly retrieve the data stored in the RFID chip about the device, the conductor system, the manufacturer, and the patient. The retrievable information does not contain any information about the current arrangement and/or the connection to the current electrode, however. In addition, the solutions explained in these documents suffer from the drawback that a comparatively large amount of energy must be expended for querying the data from the implant and for activating the chip. Additional devices used for this represent a significant SAR load (SAR=specific absorption rate−a measure for the absorption of an electromagnetic field through the tissue) for the patient.
The present invention is directed toward overcoming one or more of the above-mentioned problems.